全文获取类型
收费全文 | 305096篇 |
免费 | 1837篇 |
国内免费 | 794篇 |
专业分类
化学 | 130328篇 |
晶体学 | 4262篇 |
力学 | 18016篇 |
综合类 | 3篇 |
数学 | 64358篇 |
物理学 | 90760篇 |
出版年
2021年 | 1051篇 |
2020年 | 1213篇 |
2019年 | 1281篇 |
2018年 | 18401篇 |
2017年 | 18983篇 |
2016年 | 11232篇 |
2015年 | 3112篇 |
2014年 | 2788篇 |
2013年 | 6571篇 |
2012年 | 11880篇 |
2011年 | 25998篇 |
2010年 | 15496篇 |
2009年 | 15917篇 |
2008年 | 21043篇 |
2007年 | 25913篇 |
2006年 | 5909篇 |
2005年 | 12791篇 |
2004年 | 9200篇 |
2003年 | 9167篇 |
2002年 | 6378篇 |
2001年 | 5983篇 |
2000年 | 4579篇 |
1999年 | 3289篇 |
1998年 | 2366篇 |
1997年 | 2373篇 |
1996年 | 2425篇 |
1995年 | 2146篇 |
1994年 | 2103篇 |
1993年 | 1917篇 |
1992年 | 2357篇 |
1991年 | 2458篇 |
1990年 | 2284篇 |
1989年 | 2258篇 |
1988年 | 2242篇 |
1987年 | 2237篇 |
1986年 | 2063篇 |
1985年 | 2534篇 |
1984年 | 2571篇 |
1983年 | 2063篇 |
1982年 | 2083篇 |
1981年 | 1916篇 |
1980年 | 1901篇 |
1979年 | 2190篇 |
1978年 | 2274篇 |
1977年 | 2123篇 |
1976年 | 2082篇 |
1975年 | 1966篇 |
1974年 | 1926篇 |
1973年 | 2010篇 |
1972年 | 1301篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
T. ISHITAKEY. MIYAZAKI R. NOGUCHIH. ANDO T. MATOBA 《Journal of sound and vibration》2002,253(1):31-36
The aim of this study was to investigate the effects of exposure to whole-body vibration (WBV) and the ISO 2631/1-1997 frequency weighting on gastric motility. The gastric motility was measured by electrogastrography (EGG) in nine healthy volunteers. Sinusoidal vertical vibration at a frequency of 4, 6·3, 8, 12, 16, 31·5, or 63 Hz was given to the subjects for 10 min. The magnitude of exposure at 4 Hz was 1·0m/s2 (r.m.s.). The magnitudes of the other frequencies gave the same frequency-weighted acceleration according to ISO 2631/1-1997. The pattern of the dominant frequency histogram (DFH) was changed to a broad distribution pattern by vibration exposure. Vibration exposure had the effect of significantly reducing the percentage of time for which the dominant component had a normal rhythm and increasing the percentage of time for which there was tachygastria (p<0·05). Vibration exposure generally reduced the mean percentage of time with the dominant frequency in normal rhythm component. There was a significant difference between the condition of no vibration and exposure to 4 and 6·3 Hz of vibration frequency (p<0·05). The frequency weighting curve given in ISO 2631/1-1997 was not adequate for use in evaluating the physiological effects of WBV exposure on gastric motility. 相似文献
992.
A broad range echelle spectrograph with a CCD matrix detector is developed for different applications in atomic spectroscopy. The compact optical design in combination with a dispersive entrance slit illumination offers a low stray light level and high throughput in the UV spectral region comparable only with spectrographs of higher focal length. Ray tracing calculations for typical wavelengths and the multi-line spectrum of an iron arc show the excellent overall spectrum quality. The subtraction of two partial spectra of different steel alloys demonstrates the spectra evaluation possibilities of the CCD spectrograph. 相似文献
993.
S. A. J. Wiegers B. Tieke U. Zeitler R. Fletcher A. K. Geim J. C. Maan M. Henini 《Czechoslovak Journal of Physics》1996,46(5):2461-2462
We have investigated the interaction of phonons with a 2DEG in the FQH regime with phonon drag thermoelectric power (TEP). We find that the TEP at filling factors with the same even denominator is identical and at other even denominator filling factors they differ only by a constant. Assuming these states to be Composite Fermions (CF), we can explain our observations by extending a zero magnetic field theory for phonon drag to the CF-phonon interaction. This analysis is further corroborated by the observed T4 dependence of the CF TEP. 相似文献
994.
Yu. Dryagin N. Scalyga T. Geist 《International Journal of Infrared and Millimeter Waves》1996,17(7):1199-1204
The construction of a notch-filter for 140 GHz with very low passband insertion loss is described. It is based on a single-mode rectangular waveguide and cylindrical cavities matched to it. The typical transmission characteristic is also presented. 相似文献
995.
Graham R. Knox Peter L. Pauson Debra Willison 《Journal of organometallic chemistry》1993,450(1-2):177-184
Phenylazoferrocene undergoes nickelation and palladation exclusively on the phenyl group. Lithium phenylazocyclopentadienide has been converted into derivatives of Mo, Mn, Fe, Ru and Rh. 相似文献
996.
S. E. Kubatkin A. Ya. Tzalenchuk Z. G. Ivanov P. Delsing R. I. Shekhter T. Claeson 《JETP Letters》1996,63(2):126-132
We report on a successful attempt to fabricate a Coulomb blockade electrometer consisting of an ultrasmall YBa2Cu3O7−δ (YBCO) island coupled to two gold electrodes through a high-resistance native surface tunnel barrier. A third electrode placed
near the island was used as an electrostatic gate. Spectra typical for tunneling into the YBCO superconductor were reproducibly
measured. At temperatures below 0.5 K the low-bias conductance was suppressed by the Coulomb blockade. The blockade could
be periodically varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via
the island but without any change in the period of the Coulomb oscillations.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 112–117 (25 January 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
997.
998.
Details are given of a new method allowing an exact calculation of the spontaneous magnetization in the corner as well as along the edge at an arbitrary distance of the corner for a rectangular planar Ising ferromagnet. 相似文献
999.
Veerasingam R. Campbell R.B. Mcgrath R.T. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):688-697
A one-dimensional multispecies model of a helium filled AC plasma display cell is described. The model includes a continuity equation for each species. Poisson's equation and a circuit equation. The fill gas is helium for which the cross sections for ionization and excitation for the various atomic states are well known. The reaction rates for the different species were parametrized as functions of E/N using a zero-dimensional spatial and two velocity multispecies Boltzmann kinetic code. Calculations are performed using address and sustain voltages operating at a frequency of 50 kHz to model the pulse behavior of a dielectric barrier discharge which occurs over a time scale on the order of 200 ns or less. The code simulates multipulse behavior and shows reasonably good agreement with experimental data. The simulations show that the circuit filters out the discharge dynamics and that the pulse width of the discharge current depends on the circuit RC time constant. Using a 123 V sustain voltage, the calculated discharge current is 0.4 A with a full width at half maximum (FWHM) of 28 ns. Experimental values using a 120 V sustain voltage are 0.32 A discharge current and 42 ns FWHM 相似文献
1000.